Born in Adelaide, Oliphant was educated at the university there and at Cambridge University, England, where he obtained his PhD in 1929. He then worked at the Cavendish Laboratory in Cambridge before being appointed (1937) to the Poynting Professorship of Physics at Birmingham University. Oliphant returned to Australia in 1950 and held research chairs at the Australian National University, Canberra, until his retirement in 1967.

Hydrogen, the simplest of all atoms, normally has a nucleus of a single proton, but in 1932 Harold Urey had discovered a heavier form that he called deuterium, with a nucleus consisting of a proton and a neutron. The enlarged nucleus became known as the deuteron. In 1934 Oliphant and his collaborator Paul Harteck produced an even heavier form of hydrogen by bombarding deuterium with deuterons. This new isotope has a nucleus consisting of one proton and two neutrons (hydrogen–3). They named it ‘tritium’ and called the nucleus a ‘triton’. The isotope is radioactive with a half-life of 12.4 years and for this reason is not found in significant amounts in nature.

During World War II Oliphant did important work on the development of radar. It was in his laboratory that two German refugees, Rudolf Peierls and Otto Frisch, made some of the vital calculations and experiments that revealed the real possibility of an atomic bomb.